The federal Bureau of Reclamation began experimenting with high flows in 1996; this week's event is only the fourth experiment. The others occurred in 2004 and 2008.
But the frequency of future releases will increase to the delight of conservationists under protocols Salazar announced in May.
"We have been pitching Interior for years to do these as often as the sediment in the system warrants. They rejuvenate all the sediment-related resources," said Nikolai Lash, a program manager with the Grand Canyon Trust. Under the new protocols, high-flow releases are expected to occur as often as once or twice a year, depending on the accumulation of downstream sediments.
Scientists led by Utah State University geomorphologist Jack Schmidt will closely monitor the effects of these high flows for the next several years. Their findings will help guide a long-standing "adaptive management" strategy for the Southwest's signature river, which has carved one of the world's most scenic landscapes. Damming the river produced a windfall of electrical power, but it also wrecked the river's ecology and pushed warm-water fish species toward extinction.
"By early 1990s, the scientific community recognized it would be impossible to restore native ecosystems without controlled floods because they reintroduce disturbance into the ecosystem," said Schmidt, who now works for the U.S. Geological Survey. A professor of watershed sciences, Schmidt remains on unpaid leave from his USU appointment while he leads the Grand Canyon Monitoring and Research Center in Flagstaff, Ariz.
By disturbance, Schmidt was referring to the massive floods that once roared through Glen and Grand canyons, with flows in excess of 50,000 cfs (cubic feet per second) occurring most years and in excess of 125,000 cfs every eight years on average. Before the 1966 completion of the 710-foot-high Glen Canyon Dam, which forms Lake Powell, the Colorado pushed millions of tons of eroded sediments downstream, creating a rich network of sandbars that supported fish and riparian communities along Grand Canyon's floor, not to mention great camping spots for river runners.
The dam impounds 95 percent of the natural sediment flow, then releases water at a steady rate of 7,000 to 9,000 cfs, which prevents sediments building up at the mouths of tributaries from being pushed downstream, according Schmidt.
Now the biggest source of sediment available is the Paria River, where powerful flash floods disgorge sand loads 15 miles below the dam. Currently 500,000 metric tons, enough to bury a football field 230 feet deep, are accumulated at the mouth of the Paria.
Conservationists and scientists say this week's releases have to be carefully timed and managed to avoid doing more harm than good. Releasing too much water for too long could scour the channel of sediments and push nonnative rainbow trout into downstream stretches where they could undermine efforts to recover the endangered humpback chub.
The experiment launched early Monday when Reclamation officials increased flow through the dam's turbines to their maximum capacity 27,000 cfs. At noon, they began releasing water through the dam's four bypass outlet tubes. The flows increased through the day until reaching 42,000 cfs. That peak will be maintained for the next 24 hours, then the flows will be ramped down until the experiment's conclusion Friday.
The level of Lake Powell will drop 2.5 feet but the experiment will have no impact on the long-term level of the lake, according to Reclamation spokeswoman Lisa Iams.
The Western Area Power Administration, the federal agency that markets the dam's electricity, pegged its losses from the experiment at $1.4 million. That's the value of the power that won't be generated as a result of outflows bypassing the turbines.
But that's a small price compared with the anticipated ecological benefits of distributing the Paria's sediments downstream and the bounty of data scientists will reap over the next few months, according to Schmidt.
Glen Canyon Dam
This week's high-flow releases, which affect the Colorado River through Grand Canyon, will span five days.
For 24 hours beginning 9 p.m. Monday the outflow will be maintained at a peak of 42,300 cfs.
The test will sacrifice $1.4 million worth of electricity.
The level of Lake Powell will recede 2.5 feet
Scientists will spend the next several weeks monitoring how the high-flows redistributed sediments vital to the river's ecology.